Acoustic transformer



March 12, 1929.

P. A. ROBBINS ACOUSTIC TRANSFORMER Filed A ril 1, 192? "m" Jim,

Pai /2;:

Patented Mar. 12, 1929.

UNITED STATES PERCY A. ROBBINS, OF HIGHLAND PARK, ILLINOIS.

i ACOUSTIC TRANSFORMER.

Application filed April 1,

This invention relates to a method of and apparatus for converting the movements of a diaphragm into sound waves or vice versa.

It is well known that in ordinary loud speakers the great problem is to secure volume of tone from a diaphragm Without sacrificing quality of reproduction, and my object is to devise a method of and apparatus for securing increased amplitude in the sound waves generated by a given diaphragm, 0r conversely the securing of greater movements of the diaphragm in response to sound waves, without changes in the diaphragm which would lessen its efficiency in reproducing a wide range of sounds varying in pitch and loudness.

I attain my object by causing the vibrations of the diaphragm to be imparted to or received from a stream of a gaseous medium contacting with the diaphragm, which medium is preferably initially in a,state of compression and is allowed to expand after passing the diaphragm. Preferably also the gaseous medium contains moisture in a tinestatc of division which adds to the weight per unit of the medium and improves the result.

The invention is hereinafter more fully described and is illustrated in the accompanying drawings in which Fig. 1 is a vertical section illustrating apparatus constructed in accordance with my invention; and

Fig. 2 a similar view showing a modified form of part of the same.

Referring to Fig. 1, 1' is the chamber, with which communicates a fan or blower 2 of any suitable type whereby a continuous stream of air of substantially constant pressure may be supplied. \Vith this chan'iber connminicatcs a conduit 3, which coi'mnunicates with the smaller end of a chamber 4. which increases in cross sectional area towards its outer end in the manner common in loud speaker horns and the like.

In the construction shown the conduit 3 is integrally connected with the smaller end of the chamber 4. but this arrangement is not essential.

The conduit 3 is formed with a constricted throat 5 for a purpose which will hereinafter appear. The inner end of the conduit 3 is preferably bell-shaped. as shown. with well rounded edges to avoid the development of sound waves in the air passing through the orifice. A pear-shaped plug 6 is provided to 1927. Serial No. 180,295.

control the'orifice. This pear-shaped plug is mounted on the lever 7 is fulcrumed at one end within the chamber 1 and provided with an operating rod 8 extending through the stuffing box 9 in the top of the box. By operating the rod 8 the outflow of airafrom the chamber 1 may be controlled as desired.

Supported within thechamber l are a series of baflles 10 positioned in staggered relationship so as to form a zig-zag passageway through the chamber. These battles are preferably formed of sheets of porous material, which are maintained in a wet condition by means of water supplied to the sprinkler tubes 11, to which the upper edges of the battles are connected. The sprinkler tubes are supplied with water through the branch tubes 12, which also serve to support the sprinkler tubes. These branch tubes extend through the top of the chamber 1 and are connected with a water supply pipe 13. Separate control valves 14 are provided for the branch tubes 12.

The device, as shown, is adapted to convert undulatory electric currents into sound waves or vice versa, being provided with an electro-magnetie loud speaker unit, of which the diaphragm 15 is located adjacent the smaller end of the chamber.

The mode of operation is as follows. Air supplied by the blower 2 is compressed within the chamber 1, the pressure depending on the output of the blower and the rate at which air' is permitted to flow through the conduit 3. The air in passing through the chamber 1 takes up moisture from th surfaces of the baflies 10. and this it does the more readily since it has been slightly armed by com pression. As the air flows through the chamber. it becomes cooled due to the absorption of heat by evaporation of the moisture. The weight of the air per unit of volume thus be comes greater. There is thus delivered to the opening of the conduit I, a stream of a gaseous medium of a greater density than that of the atmosphere.

in the delicate balance of pressure. temperature and volume, any disturbance of one factor immediately affects the others and the compression of the air by its own momentum in the constricted throat 5 and the loss of heat due to work expended in overcoming friction in the throat will causea slight precipitation of moisture in the gaseous stream in the form of a mist. A stream of air under pressure and containing relatively heavy articles of moisture thus flows over the surface of the diaphragm 15 so that the vibrations of the diaphragm are imparted to a medium denser than atmospheric air, which is a condition favorable for the taking up by the gaseous stream of the vibrations of the diaphragm. After passing the diaphragm, the moisture laden air expands in the horn like chamber 4, some of the particles of moisture being revaporized and, as the moisture laden air emerges from the horn, there is a further expansion and re-vaporization of moisture due to the reduction of pressure and the taking up of heat from the surrounding atmosphere.

It will be seen that the valuable results obtained by the use of my method and aparatus are due to the fact thatthe diaphragm 1s operating in a relatively dense medium, and that this dense medium is subsequently expanded in volume and cross sectional area,

so that, while it is not possible to increase the store of energy of a sound wave after it has left its source, yet it is possible to increase its phonetic energy, and this present invention takes advantage of that fact. i

The invention may be applied with slight modifications to any form of acoustic transformer, and a modification to adapt the device to the cone type of loud speaker is illustrated in Fig. 2. In this form 16 is a vibratable cone adapted to bevibrated by means of the electro-magnetic device 17 of any known type. The conduit 3% corresponds to the conduit 3. \Vhilea space 45* between the diaphragm 16 and the bell 18 corresponds to the e"; amber 4. This bell 18 is preferably formed integral with the inner end of the conduit 3 and is so shaped that the space between the bell and the cone gradually increases in cross sectional area towards the base of the cone. A constricted throat 5 is formed by means of the cone-shaped plug 19 located at the inner end of the conduit 3 and preferably supported from the cone 16.

The mode of operation with this construction, it will be seen, is substantially the same as with the construction illustrated in Fig. 1.

Many other modifications are possible according as the device is intended for use in making or utilizing phonographic records or receiving or transmitting sounds electrically.

\Vhat I claim is:

1. The method of imparting vibrations from a vibratable diaphragm to the atmosphere or vice versa, which consists in employing as the transferring medium a stream of a gaseous medium passing over and contacting with the diaphragm.

2. The method of imparting vibrations from a vibratable diaphragm to the atmosphere or vice versa, which consists in employing as the transferring medium a stream of a compressed gaseous medium passing over and contacting with the diaphragm and expanding in contact with the atmosphere.

3. The method of imparting vibrations from a vibratable diaphragm to the atmosphere or vice versa, which consists in employing as the transferring medium a stream of a gaseous medium passing over and contacting with the diaphragm and being of greater density than .the atmosphere.

4. The method of imparting vibrations from a vibratable diaphragmto the atmosphere or vice versa, which consists in employing as the transferring medium a stream of a gaseous medium containing water in a fine state of division and contacting with the diaphragm. Y

5'. The method of imparting vibrations from a vibratable diaphragm to the atmosphere or vice versa, which consists in employing as the transferring medium a stream of a compressed gaseous medium containing water in a fine state of division and contacting with the diaphragm and expanding in contact with the atmosphere.

6. The method of imparting vibrations from a vibratable diaphragm to the atmosphere or vice versa, which consists in employing as the transferring medium a stream of a gaseous medium containing Water in a fine state of division and contacting with the diaphragm and being of greater density than the atmosphere.

7. The method of imparting vibrations from a vibratable diaphragm to the atmosphere, which consists in imparting the vibrations of the diaphragm to a stream of a gaseous medium passing overand contacting with said diaphragm and expanding in cross sectional area after passing the same.

8. The method of imparting vibrations from a vibratable diaphragm to the atmosphere, which consists in imparting the vibrations of the diaphragm to a stream of a gaseous medium expanding in cross sectional area after passing the diaphragm and initially containing water in a fine state of division.

9. The method of imparting vibrations from a vibratable. diaphragm to the atmosphere, which consists in imparting the vib'rations of the diaphragm to a stream of a gaseous medium passing over and contacting with said diaphragm and expanding in volume and in cross sectional area after passing the same.

10. The method of imparting vibrations from a vibratable diaphragm to the atmos phere, whiih consists in imparting the vibrations of the diaphragm to a stream'of a gaseous medium expanding in volume and in cross sectional area after passing the diaphragm and initially containing water in a fine state of division.

11. The method of imparting vibrations from a vibratable diaphragm to the atmos phere, which consists in imparting the vibrations of the diaphragm to a stream of a gaseous medium passing over and contacting with said diaphragm and expanding in cross sectional area after passing the same and being initially at least of greater density than the atmosphere.

12. The method of imparting vibrations from a vibratable diaphragm to the atmosphere, which consists in imparting moisture to a stream of air, causing a condensation of the moisture in fine particles in the stream, passing the inoisture laden air over the diaphrgm and subsequently expanding the stream of air in cross sectional area in contact with the atmosphere.

13. The method of imparting vibrations from a vibratable diaphragm to the atmosphere, which consists in producing a stream of slightly compressed moisture containing air, causing a condensation of the moisture in fine particles in the stream, passing the moisture laden air over the diaphragm, and subsequently expanding the stream of air in volume and cross sectional area in contact with the atmosphere.

14. The method of impartingvibrations from a vibratable diaphragm to the atmosphere, which consists in imparting moisture to a stream of air, causing a condensation of the moisture in tine particles in the stream by contracting the cross sectional area of the stream, passing the' moistureladen air over the diaphragm and sub.--1equently expanding the stream of air in cross sectional area in contact with the atmosphere.

of slightly compressed moisture containing air, causing a condensation of the moisture in fine particles in the stream by contracting the cross sectional area of the stream, passing the moisture laden airover the diaphragm, and subsequently expanding the stream of air in volume and cross sectional area in contact with the atmosphere.

16. An acoustic transformer comprising a chamber increasing in cross sectional area from one end towards the other; a vibratable diaphragm at the smaller end of the chamber; and means for continuously forcing a gaseous .medium into the smaller end of the chamber into contact with and past the diaphragm.

17. An acoustic transformer comprising a chamber increasing in cross sectional area from one end towards the other; a vibratable diaphragm at the smaller end of the chamber; a conduit communicating with the smaller end of the chamber having a constricted throat adjacent thereto; and means for continuously .forcing a gaseous medium into the smaller end of the conduit into contact with "and'past the diaphragm. i

18. An acoustic transformer comprising a chamber increasing in cross sectional area from one end towards the other; a vibratable diaphragm at the smaller end of the chamber; means for continuously forcing a gaseous medium into the smaller end of the chamber into contact with and past the diaphragm; and means for adding moisture to the gaseous medium passing to the chamber.

Signed at Highland Park, Ill., this third day of March, 1927.

PERCY A. ROBBINS. 

